Finding his soulmate was easy. In his attempts to learn the rules of socializing properly, Sai had developed the habit of repeating back every new piece of information he was given. Repetition helped with memory, after all. The first time he was introduced to Aburame Shino he had repeated the name in a quiet mumble and that was that, he had found the person his soul was meant to be bound to. Shino described the feeling of

knowing

as a thousand insects vibrating through every inch of his body while feeling the jolt of a low level raiton at the same time.

Sai would have loved to experience that feeling for himself. And that would have been easy if only he knew what his own name was. Even years later it seemed ROOT was still finding ways to take more away from him.